Passage Based/ SA-I SA-II LA S

QUESTION PAPER DESIGN 2020-21#

Passage based/ SA-I SA-II LA S. No. Chapter Total MCQs/A & R (1 mark) (2 marks) (3 marks) (5 marks) 1. The Solid State 1(1) 1(2) 1(3) – 2. Solutions 2(2) 1(2) – – 3. Electrochemistry 1(1) – – 1(5) 11(24) 4. Chemical Kinetics – 2(4) – – 5. Surface Chemistry 1(4) – – – 6. The p-Block Elements 1(1) 1(2) 1(3) 1(5) 7. The d- and f-Block Elements 2(2) – 1(3) – 9(19) 8. Coordination Compounds 1(1) 1(2) – – 9. Haloalkanes and Haloarenes 1(1) 2(4) – – 10. Alcohols, Phenols and Ethers 2(5) 1(2) – – 11. Aldehydes, Ketones and Carboxylic Acids 1(1) – – 1(5) 13(27) 12. Amines 1(1) – 1(3) – 13. Biomolecules 2(2) – 1(3) – Total 16(22) 9(18) 5(15) 3(15) 33(70)

1. The Solid State ��1 2. Solutions ��12 3. Electrochemistry ��25 4. Chemical Kinetics ��35 5. Surface Chemistry ��48 6. General Principles and Processes of Isolation of Elements 7. The p-Block Elements ��56 8. The d- and f-Block Elements ��65 9. Coordination Compounds ��72 10. Haloalkanes and Haloarenes ��84 11. Alcohols, Phenols and Ethers ��98 12. Aldehydes, Ketones and Carboxylic Acids ��111 13. Amines ��126 14. Biomolecules ��137 15. Polymers 16. Chemistry in Everyday Life

This chapter is not a part of the Board Examination 2020-21 syllabus #For latest information please refer to www.cbse.nic.in CHAPTER Aldehydes, Ketones 12 and Carboxylic Acids

CASE STUDY / PASSAGE BASED QUESTIONS

Read the passage given below and answer the following questions : The addition reaction of enol or enolate to the carbonyl functional group of aldehyde or ketone is known as aldol addition. The b-hydroxyaldehyde or b-hydroxyketone so obtained undergo dehydration in second step to produce a conjugated enone. The first part of reaction is an addition reaction and the second part is an elimination reaction. Syllabus Carbonyl compound having a-hydrogen undergoes aldol condensation reaction. O O Aldehydes and – Ketones : Nomen- OH 2CH3CH2 C H D CH3CH2CH CC H clature, nature of carbonyl group, CH3 methods of prepa- Mechanism : ration, physical O O and chemical HO + HCCH H 3C CHH C H properties, mecha- –H2O nism of nucleo- CH3 philic addition, O O O O reactivity of alpha hydrogen in alde- CH3CH2 C +CH C H CH3CH2 CH CH C H hydes, uses. H CH CH Carboxylic Acids : 3 3 Nomenclature, OH O O acidic nature, H2O –H2O – CH CH CH CH C H CH CH CH CC H methods of prepa- –OH 3 2 D 3 2 CH ration, physical CH3 3 and chemical The following questions are multiple choice questions. Choose the most appropriate properties, uses. answer : (i) Condensation reaction is the reverse of which of the following reaction? (a) Lock and key hypothesis (b) Oxidation (c) Hydrolysis (d) Glycogen formation (ii) Which of the following compounds would be the main product of an aldol condensation of acetaldehyde and acetone? (a) CH3CH CHCHO (b) CH3CH CHCOCH3 (c) (CH3)2C CHCHO (d) (CH3)2C CHCOCH3 112 Chemistry | Class 12

(iii) Which combination of carbonyl compounds gives phenyl vinyl ketone by an aldol condensation? O

Ph (a) Acetophenone and Formaldehyde (b) Acetophenone and acetaldehyde (c) Benzaldehyde and acetaldehyde (d) Benzaldehyde and acetone (iv) Which of the following will undergo aldol condensation?

(a) HCHO (b) CH3CH2OH (c) C6H5CHO (d) CH3CH2CHO OR Which of the following does not undergo aldol condensation ?

(a) CH3CHO (b) CH3CH2CHO (c) CH3COCH3 (d) C6H5CHO 2

Read the passage given below and answer the following questions : When an aldehyde with no a-hydrogen reacts with concentrated aqueous NaOH, half the aldehyde is converted to carboxylic acid salt and other half is converted to an alcohol. In other words, half of the reactant is oxidized and other half is reduced. This reaction is known as Cannizzaro reaction. O O Conc. NaOH 2 C H C ONa + CH2OH Mechanism : O O O Ph C H OH Ph CCH + Ph

OH H O O O OH Ph C + H C PhPh C + H C Ph O H O H H The following questions are multiple choice questions. Choose the most appropriate answer : (i) A mixture of benzaldehyde and formaldehyde on heating with aqueous NaOH solution gives (a) benzyl alcohol and sodium formate (b) sodium benzoate and methyl alcohol (c) sodium benzoate and sodium formate (d) benzyl alcohol and methyl alcohol. (ii) Which of the following compounds will undergo Cannizzaro reaction?

(a) CH3CHO (b) CH3COCH3 (c) C6H5CHO (d) C6H5CH2CHO (iii) Trichloroacetaldehyde is subjected to Cannizzaro’s reaction by using NaOH. The mixture of the products contains sodium trichloroacetate ion and another compound. The other compounds is (a) 2, 2, 2-trichloroethanol (b) trichloromethanol (c) 2, 2, 2-trichloropropanol (d) chloroform. OR In Cannizzaro reaction given below : – OH – 2PhCHO PhCH2OH + PhCO2 the slowest step is Aldehydes, Ketones and Carboxylic Acids 113

(a) the attack –OH at the carboxyl group (b) the transfer of hydride to the carbonyl group (c) the abstraction of proton from the carboxylic group

(d) the deprotonation of PhCH2OH. (iv) Which of the following reaction will not result in the formation of carbon-carbon bonds? (a) Cannizzaro reaction (b) Wurtz reaction (c) Reimer-Tiemann reaction (d) Friedel-Crafts’ acylation

Read the passage given below and answer the following questions : A tertiary alcohol H upon acid catalysed dehydration gives a product I. Ozonolysis of I leads to compounds J and K. Compound J upon reaction with KOH gives benzyl alcohol and a compound L, whereas K on reaction with KOH gives only M. O H3C Ph M = Ph H The following questions are multiple choice questions. Choose the most appropriate answer : (i) Compound H is formed by the reaction of O O + PhMgBr + PhCH2MgBr (a) Ph H (b) Ph CH3 O O Me + + PhCH2MgBr (c) Ph H (d) Ph H Ph MgBr OR

The structure of compound I is Ph CH Ph Ph CH HC CH 3 HC3 3 3 3 (a) (b) (c) (d) H Ph H Ph H CH2Ph Ph H (ii) The structures of compound J, K and L, respectively, are – + – + (a) PhCOCH3, PhCH2COCH3 and PhCH2COO K (b) PhCHO, PhCH2CHO and PhCOO K – + – + (c) PhCOCH3, PhCH2CHO and CH3COO K (d) PhCHO, PhCOCH3 and PhCOO K (iii) When (J) is treated with acetic anhydride, in the presence of corresponding salt of an acid, the product obtained is (a) cinnamic acid (b) crotonic acid (c) maleic acid (d) benzylic acid. (iv) Which of the following statements is correct for compound (K)?

(a) It reacts with alkaline KMnO4 followed by acidic hydrolysis and forms benzoic acid. (b) It reacts with iodine and NaOH to form triiodomethane. (c) It is prepared by the reaction of benzene with benzoyl chloride in presence of anhydrous aluminium chloride. (d) It reacts with freshly prepared ammoniacal silver nitrate solution. 114 Chemistry | Class 12

Read the passage given below and answer the following questions : Carboxylic acids dissociate in water to give carboxylate ion and hydronium ion. – + RCOOH + H2O RCOO +H3O The acidity of carboxyl group is due to the presence of positive charge on oxygen which liberates proton. The carboxylate ion formed is resonance stabilised. O – O – O O–1/2

e.g., C R C H2O O

+ R C R C R C R O O H O H –H3O – + O O–1/2 Carboxylic acids are stronger acids than phenols. Electron withdrawing groups (EWG) increase the acidity of carboxylic acids by stabilising the conjugate base through delocalisation of negative charge by inductive and/or resonance effects. Electron donating group (EDG) decrease the acidity by destabilising the conjugate base. The following questions are multiple choice questions. Choose the most appropriate answer : (i) Which of the following reactions is showing the acidic property of carboxylic acid? O O O O

(a) 2CR OH + 2Na 2CR ONa + H2 (b) R C OH + NaOH R C ONa + HO2 O O

(c) 2CR OH + 2NaC23O 2CR ONa (d) All of these. + HO22 + CO (ii) Which one of the following is the correct order of acidic strength?

(a) CF3COOH > CHCl2COOH > HCOOH > C6H5CH2COOH > CH3COOH (b) CH3COOH > HCOOH > CF3COOH > CHCl2COOH > C6H5CH2COOH (c) HCOOH > C6H5CH2COOH > CF3COOH > CHCl2COOH > CH3COOH (d) CF3COOH > CH3COOH > HCOOH > CHCl2COOH > C6H5CH2COOH OR The acidic strength of the given compounds follows the order : O O

:: I. CH3 CH CH C OH II. CH3 O CH CH C OH

III. (a) II > III > I (b) III > II > I (c) II > I > III (d) I > II > III (iii) Which of the following acids has the smallest dissociation constant?

(a) CH3CHFCOOH (b) FCH2CH2COOH (c) BrCH2CH2COOH (d) CH3CHBrCOOH (iv) The correct order of acidity for the following compounds is

(a) I > II > III > IV (b) III > I > II > IV (c) III > IV > II > I (d) I > III > IV> II Aldehydes, Ketones and Carboxylic Acids 115

Read the passage given below and answer the following questions : O

Aldehydes and ketones having acetyl group CH3 C are oxidised by sodium hypohalate (NaOX) or – halogen and alkali (X2 + OH ) to corresponding sodium salt having one carbon atoms less than the carbonyl compound and give a haloform. O O NaOX R C CH3 R C ONa + CHX3 (X = Cl, Br, I) or X2 + NaOH

Sodium hypoiodite (NaOI) when treated with compounds containing CH3CO group gives yellow precipitate of iodoform. Haloform reaction does not affect a carbon-carbon double bond present in the compound. The following questions are multiple choice questions. Choose the most appropriate answer : (i) Which of the following compounds will give positive iodoform test? (a) Isopropyl alcohol (b) Propionaldehyde (c) Ethylphenyl ketone (d) Benzyl alcohol (ii) Which of the following compounds is not formed in iodoform reaction of acetone?

(a) CH3COCH2I (b) ICH2COCH2I (c) CH3COCHI2 (d) CH3COCI3 (iii) For the given set of reactions,

starting compound A corresponds to O O O O (a) (b) (c) (d) COCH CH2COOH CH2COOH 3 COCH3 OR In the following reaction sequence, the correct structures of E, F and G are

(* implies 13C labelled carbon) E O F O G O O (a) = = – + = CHI3 (b) E = F = G = CHI Ph ONa * – + 3 Ph * CH3 * Ph CH3 Ph ONa O O O O E F G * E F G * (c) = * = – + = CHI3 (d) = * = – + = CHI3 Ph CH3 Ph ONa Ph CH3 Ph O Na

(iv) An organic compound ‘A’ has the molecular formula C3H6O. It undergoes iodoform test. When saturated with HCl it gives ‘B’ of molecular formula C9H14O. ‘A’ and ‘B’ respectively are (a) propanal and mesityl oxide (b) propanone and mesityl oxide (c) propanone and 2,6-dimethyl-2,5-hepta-dien‑4‑one (d) propanone and propionaldehyde. 116 Chemistry | Class 12

Read the passage given below and answer the following questions :

(A), (B) and (C) are three non-cyclic functional isomers of a carbonyl compound with molecular formula C4H8O. Isomers (A) and (C) give positive Tollen’s test whereas isomer (B) does not give Tollen’s test but gives positive iodoform test. Isomers (A) and (B) on reduction with Zn(Hg)/conc. HCl give the same product (D). The following questions are multiple choice questions. Choose the most appropriate answer : (i) Compound A is

(a) CH3 CH CHO (b) CH3CH2CH2CHO

CH3 O

(c) CH3 C CH2 CH3 (d) none of these. OR Compound (C) is (a) iso-butyraldehyde (b) butyraldehyde (c) crotonaldehyde (d) acrolein. (ii) Compound (B) can be obtained by dil. H2SO4 + HgSO4 (a) CH3 C C CH2 CH3 Dry distill 333 K (b) (CH3CH2COO)2Ca O B2H6/THF 3 (c) CH3 C C CH3 (d) CH3 CH CH CH3 H2O2/NaOH Zn/H2O (iii) Out of (A), (B) and (C) isomers, which one is least reactive towards addition of HCN? (a) A (b) B (c) C (d) All are equally reactive (iv) What will be the product when (B) reacts with ethylene glycol in presence of HCl gas?

(a) (b) (c) (d) None of these.

Read the passage given below and answer the following questions :

Aldehydes and ketones are reduced to primary and secondary alcohols respectively by NaBH4 or LiAlH4 as

well as catalytic hydrogenation. The carbonyl group of aldehydes and ketones is reduced to CH2 group on treatment with Zn-Hg and conc. HCl (Clemmensen reduction) or with hydrazine followed by NaOH or KOH in highly boiling solvent such as ethylene glycol (Wolff-Kishner reduction). Aldehydes differ from ketones in their oxidation reactions. Aldehydes are easily oxidised to carboxylic acids on treatment with HNO3, KMnO4, K2Cr2O7 etc. Even mild oxidising agents mainly Tollens’ reagent and Fehling’s solution also oxidise aldehydes. Ketones are generally oxidised under vigorous conditions i.e., strong oxidising agents and at elevated temperatures, to give mixture of carboxylic acids having lesser number of C-atoms than the parent ketone. The following questions are multiple choice questions. Choose the most appropriate answer :

(i) Which of the following cannot be made by reduction of ketone or aldehyde with NaBH4 in methanol? (a) 1-Butanol (b) 2-Butanol (c) 2-Methyl-1-propanol (d) 2-Methyl-2-propanol Aldehydes, Ketones and Carboxylic Acids 117

(ii) The carbonyl compound producing an optically active product by reaction with LiAlH4 is (a) propanone (b) butanone (c) 3-pentanone (d) benzophenone.

(iii) A substance C4H10O(X) yields on oxidation a compound C4H8O which gives an oxime and a positive iodoform test. The substance X on treatment with conc. H2SO4 gives C4H8. The structure of the compound (X) is

(a) CH3CH2CH2CH2OH (b) CH3CH(OH)CH2CH3 (c) (CH3)3COH (d) CH3CH2 O CH2CH3 O 14 (iv) In the oxidation of by acidified K2Cr2O7, the products are O O 14 14 CH COH and CH CH COOH (a) 33–– 2 (b) CH32(CH )C––OH andCHCH2COOH 14 (c) CH322CH CH COOH+HCOOH (d) none of these. OR The appropriate reagent for the following transformation is

– (a) NH2NH2, OH (b) NaBH4 (c) H2/Ni (d) AlCl3 8

Read the passage given below and answer the following questions : Carboxylic acids having an a-hydrogen atom when treated with chlorine or bromine in the presence of small amount of red phosphorus gives a-halocarboxylic acids. The reaction is known as Hell-Volhard-Zelinsky reaction. red P R CH2 COOH + X2 R CH COOH X (X = Cl, Br) When sodium salt of carboxylic acid is heated with soda lime it loses carbon dioxide and gives hydrocarbon with less number of C-atoms. NaOH + CaO R COOH NaOH R COONa R H + Na CO D 2 3 Carboxylic Sod. Alkane acid carboxylate In these questions (Q. No. i-iv), a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices. (a) Assertion and reason both are correct statements and reason is correct explanation for assertion. (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion. (c) Assertion is correct statement but reason is wrong statement. (d) Assertion is wrong statement but reason is correct statement.

(i) Assertion : (CH3)3CCOOH does not give H.V.Z reaction. Reason : (CH3)3CCOOH does not have a-hydrogen atom. 118 Chemistry | Class 12

(ii) Assertion : H.V.Z. reaction involves the treatment of carboxylic acids having a-hydrogens with Cl2 or Br2 in presence of small amount of red phosphorus. Reason : Phosphorus reacts with halogens to form phosphorus trihalides. OR

Assertion : Propionic acid with Br2/P yields CH2Br — CHBr — COOH. Reason : Propionic acid has two a-hydrogen atoms.

(iii) Assertion : C6H5COCH2COOH undergoes decarboxylation easily than C6H5COCOOH. Reason : C6H5COCH2COOH is a b-keto acid. (iv) Assertion : On heating 3-methylbutanoic acid with soda lime, isobutane is obtained. Reason : Soda lime is a mixture of NaOH + CaO in the ratio 3 : 1.

Read the passage given below and answer the following questions : Fehling’s reagent : Fehling’s reagent is a mixture of two solutions. Fehling’s solution A is aqueous copper sulphate solution. Fehling’s solution B is alkaline sodium potassium tartarate (Rochelle salt). CH(OH)COONa CuSO4( aq ) + CH(OH)COOK It is a mild oxidising agent. It is weaker than Tollens’ reagent. It oxidises only aliphatic aldehydes to carboxylate ions and itself gets reduced to reddish brown precipitate of cuprous oxide. Aromatic aldehydes do not respond to Fehling’s test. This reaction is used for the test of aliphatic aldehydes known as Fehling’s reagent test. In these questions (Q. No. i-iv), a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices. (a) Assertion and reason both are correct statements and reason is correct explanation for assertion. (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion. (c) Assertion is correct statement but reason is wrong statement. (d) Assertion is wrong statement but reason is correct statement. (i) Assertion : Fehling’s solution can be used to distinguish between acetaldehyde and acetone. Reason : Fehling’s reagent is a mixture of two solutions. (ii) Assertion : Aromatic aldehydes can be distinguished from aliphatic aldehydes by Fehling’s solution. Reason : Aromatic aldehydes reduce Fehling’s solution, but aliphatic aldehydes do not. OR

Assertion : Fehling’s solution oxidises acetaldehyde to acetic acid but not benzaldehyde to benzoic acid. Reason : The C — H bond of – CHO group in benzaldehyde is stronger than in acetaldehyde.

(iii) Assertion : CH3CHO and C6H5CH2CHO cannot be distinguished chemically by Fehling’s solution.

Reason : CH3CHO and C6H5CH2CHO can be distinguished by iodoform test. (iv) Assertion : Formaldehyde, when heated with Fehling’s reagent produces a reddish brown ppt. of Cu. Reason : Fehling’s reagent oxidises formaldehyde to formate ion. Aldehydes, Ketones and Carboxylic Acids 119

Read the passage given below and answer the following questions : Aldehydes and ketones undergo nucleophilic addition reactions. Nu Nu R1 + Nu E+ C O C C R2 R1 O R1 OE R2 R2 Carbonyl carbon is electron deficient hence acts as an electrophile. Nucleophile attacks on the electrophilic carbon atom of the carbonyl group from a direction perpendicular to the plane of the molecule.

Nu Nu Nu +d d R1 Slow Fast C O C + C R2 H R1 O R1 OH R2 R2 In this process, hybridisation of carbon atom changes from sp2 to sp3 and a tetrahedral alkoxide ion is formed as intermediate. This intermediate captures proton from the reaction medium to give the neutral product. Aldehydes are generally more reactive than ketones in nucleophilic addition reactions. In these questions (Q. No. i-iv), a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices. (a) Assertion and reason both are correct statements and reason is correct explanation for assertion. (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion. (c) Assertion is correct statement but reason is wrong statement. (d) Assertion is wrong statement but reason is correct statement. (i) Assertion : Benzaldehyde is more reactive than ethanal towards nucleophilic attack. Reason : The overall effect of –I and +R effect of phenyl group decreases the electron density on the carbon atom of C O group in benzaldehyde.

(ii) Assertion : (CH3)3CCOC(CH3)3 and acetone can be distinguished by the reaction with NaHSO3. – Reason : HSO3 is the nucleophile in bisulphite addition.

COCH3

(iii) Assertion : Ease of nucleophilic addition of the compounds (I), CH3CHO(II) and CH3COCH3(III) is I > II > III. Reason : Aldehydes and ketones undergo nucleophilic addition reactions. OR

Assertion : The formation of cyanohydrin from an aldehyde or ketone occurs very slowly with pure HCN. This reaction is catalysed by a base. Reason : Base generates CN– ion which is a stronger nucleophile. CHO CHO

(iv) Assertion : is more reactive towards nucleophilic addition reaction than .

NO2 CH3 Reason : Reactivity of carbonyl group is due to electrophilic nature of carbonyl carbon. 120 Chemistry | Class 12

ASSERTION & REASON

In these questions, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices. (a) Assertion and reason both are correct statements and reason is correct explanation for assertion. (b) Assertion and reason both are correct statements but reason is not correct explanation for assertion. (c) Assertion is correct statement but reason is wrong statement. (d) Assertion is wrong statement but reason is correct statement. 11. Assertion : Hydrogen bonding in carboxylic acids is stronger than alcohols. Reason : Highly branched carboxylic acids are more acidic than unbranched acids. 12. Assertion : Cross aldol condensation of ethanal and propanal gives a mixture of four products. Reason : Ethanal and propanal, both contain a-hydrogen atom. 13. Assertion : Boiling point of aldehydes lie in between parent alkanes and corresponding alcohols. Reason : Aldehydes cannot form intermolecular hydrogen bonds like alcohols.

14. Assertion : NaHSO3 is used for the purification of carbonyl compounds. Reason : They are used in the blending of perfumes and flavouring agents. 15. Assertion : m-Chlorobenzoic acid is a stronger acid than p-chlorobenzoic acid. Reason : In m-chlorobenzoic acid both – I-effect and +R-effect of Cl operate but in p-chlorobenzoic acid only +R-effect of Cl operates. 16. Assertion : Presence of acids and bases activates carbonyl compounds for reaction. Reason : Carbonyl compounds possess positive and negative centres and provide a seat for electrophilic and nucleophilic attack. 17. Assertion : Formic acid is a stronger acid than benzoic acid. Reason : pKa of formic acid is lower than that of benzoic acid. 18. Assertion : Aldol condensation can be catalysed both by acids and bases. Reason : b-Hydroxy aldehydes or ketones readily undergo acid catalysed dehydration. 19. Assertion : Carboxylic acids have higher boiling points than alkanes. Reason : Carboxylic acids are resonance hybrids. 20. Assertion : Lower aldehydes and ketones are soluble in water but the solubility decreases as the molecular mass increases. Reason : Distinction between aldehydes and ketones can be done by Tollens’ test. 21. Assertion : Fluoroacetic acid is stronger than chloroacetic acid. Reason : Carboxylic acids are weak acids and turn blue litmus red. 22. Assertion : Ketones can be converted into acids by haloform reaction. Reason : Addition of Grignard reagents to dry ice followed by hydrolysis gives ketones. 23. Assertion : Benzaldehyde undergoes aldol condensation. Reason : Aldehydes having a-hydrogen atom undergo aldol condensation. 24. Assertion : Acetic acid in vapour state shows a molecular mass of 120. Reason : It undergoes intermolecular hydrogen bonding. 25. Assertion : Nitration of benzoic acid gives m-nitrobenzoic acid. Reason : Carboxyl group increases the electron density at the meta-position. Aldehydes, Ketones and Carboxylic Acids 121

26. Assertion : Carboxylic acids are stabilised by resonance. Reason : Chloroacetic acid is weaker than acetic acid.

27. Assertion : a-Hydrogen atoms in aldehydes and ketones are acidic. Reason : The anion left after the removal of a-hydrogen is stabilised by inductive effect.

28. Assertion : During reaction of carboxylic acids with NaHCO3, the CO2 evolved comes from carboxylic acid

and not from NaHCO3. Reason : Carbonic acid is a weaker acid than carboxylic acid.

29. Assertion : o-Substituted benzoic acids are generally stronger acids than benzoic acids. Reason : Increased strength is due to ortho-effect.

30. Assertion : Aromatic aldehydes and formaldehyde undergo Cannizzaro reaction. Reason : Aromatic aldehydes are almost as reactive as formaldehyde.

1. (i) (c) :Condensation reaction is the reverse of Cl O Cl O hydrolysis, which splits a chemical entity into two NaOH 2Cl C C Cl C C parts through the action of the polar water molecule. H O– Cl Cl (ii) (b) : CH33CHO + CH COCH3 trichloroacetate ion Cl OH CH32 CH(OH)CH COCH3

D –H2 O + Cl C CH2

CH3 CH CHCOCH3 Cl (iii) (a) 2, 2, 2-trichloroethanol (iv) (d) OR (b) : Hydride transfer is the slowest step. OR – O O (d) : Benzaldehyde(C6H5CHO) with no a-hydrogen cannot undergo aldol condensation. slow Ph OH +C Ph CH step 2. (i) (a) : It is an example of cross Cannizzaro H reaction where aromatic aldehyde gets reduced to O alcohol and aliphatic aldehyde gets oxidised to its Ph OH+C Ph CH O– sodium salt (both aldehydes must not contain any 2 a-hydrogen). (iv) (a) : C C bond is not formed in Cannizzaro reaction while other reactions result in the formation CHO CH2OH of C C bond. ∆ + NaOH + HCHO + HCOONa 3. (i)(b) : O OH (ii) (c) Ph C CH + PhCH MgBr Ph C CH –– 3 2 –– 3 (iii) (a) : The Cannizzaro product of given reaction CH Ph 2 – yields 2, 2, 2-trichloroethanol. ()H 122 Chemistry | Class 12

OR stronger acid than (IV) because at m-position, –OH OH group cannot exert its +R effect but can only exert H+ its –I effect while at p-position, –OH group exerts its (a) : Ph CC2 PhH Ph CH C Ph –H2 O strong +R effect. ()H CH3 ()I CH3 Thus, the correct order of acidity is : Ozonolysis I > II > III > IV (ii)(d) : PhCH C Ph PhCHO + Ph C O ()J 5. (i) (a) : Iodoform test is given by the organic CH3 CH3 O OH ()I ()K compounds having CH —C— or CH —CH— group. KOH 3 3 Ph CHO Ph CH OH + Ph COO–+ K Cannizzaro 2 CH3—CH— OH : Isopropyl alcohol ()J reaction ()L CH3

CH3CH2CHO : Propionaldehyde O

C2H5—C—C6H5 : Ethylphenyl ketone

C6H5 — CH2—OH : Benzyl alcohol (iii) (a) : Therefore, isopropyl alcohol will give positive A iodoform test. C6H5 CH CH COOH Cinnamic acid (ii) (b) : Iodoform reaction of acetone occurs in following steps : (iv) (b) 4. (i) (d) : All the reactions are showing the acidic properties of carboxylic acid. Carboxylic acid forms the sodium salts with all i.e., alkali metals, NaOH and

Na2CO3 etc. and removes the acidic proton from the carboxylic acid.

(ii) (a) : In general, greater the +I effect of the group attached to the carboxyl group, lesser will be the acidic strength and greater the –I effect of the group, greater will be acidic strength. As number of halogen atoms (iii) (c) : Given reagents indicate the presence of and electronegativity of halogen atom increases, acidic COCH group in the starting compound A. Further, strength increases. 3 since the COOH group introduced in B due to Thus, correct order of acidic strength is iodoform reaction is absent in the final product, CF COOH > CHCl COOH > HCOOH > 3 2 B should be a b-keto acid. Hence, A should have C H CH COOH > CH COOH 6 5 2 3 structure given in option (c). OR O O O (i) NaOI Heat + (d) (ii) H (–CO2) COCH3 COOH (iii) (c) : Stronger –I group attached closer to – COOH (A) (B) makes the acid stronger, i.e., acid has the larger OR dissociation constant. –Br shows poor (–I) effect and O O O also far away from –COOH group i.e., option (c) has I2 Heat * smallest dissociation constant. (d) : Ph * OH Ph CH3 NaOH β-keto Acid (E) (iv) (a) : Due to ortho-effect, (I) and (II) are stronger O –+ * acids than (III) and (IV). Due to two ortho-hydroxyl Ph ONa + CHI3 groups in (I), it is stronger acid than (II). (III) is a (F) (G) Aldehydes, Ketones and Carboxylic Acids 123

(iv) (c) : Since compound A(C3H6O) undergoes iodoform test, it must be CH3COCH3 (propanone). Further, the compound ‘B’ obtained from ‘A’ has three times more the number of carbon atoms as in ‘A’ 7. (i) (d) : 2-Methyl-2-propanol is It (propanone), ‘B’ must be phorone, i.e., 2, 6-dimethyl-2, 5-heptadien‑4-one. (CH3)2C O + H3CCOCH3 + O C(CH3)2 cannot be obtained by reduction of an aldehyde or A, propanone (3 molecules) ketone with NaBH . HCl 4 (CH3)2C CHCOCH C(CH3)2 2,6-dimethyl-2,5-heptadien-4-one (ii) (b) : 6. (i) (b) : As (A) and (C) gives positive Tollens’ test thus these two should be aldehydes while (B) should be a ketone (does not give Tollen’s test) with C CH3 O group (as it gives positive iodoform test). Three isomers are, O

CH3CH2CH2CHO, CH3 C CH2 CH3 (A) (B) CH3 CH CHO

CH3 (C) Zn(Hg)/conc. HCl CH3CH2CH2CHO CH3CH2CH2CH3 (A) (D) O Zn(Hg)/conc. HCl CH3 C CH2 CH3 (B) CH CH CH CH 3 2 2 3 (iii) (b) : (D)

OR 2-Butanone forms oxime on reaction with (d) hydroxylamine (NH2OH) and also gives positive iodoform test. B H (ii) (c) : 6CH C C CH 2 6 3 3 THF H2O2 2 CH CH C B 6CH CH CCH 3 NaOH 3 3

H3C 3 OH Tautomerisation (iv) (a) :

6CH3CH2 C CH3 O (iii) (b) : (B) is least reactive among the three isomers towards addition of HCN. Aldehydes are more reactive than ketones towards nucleophilic addition reactions. OR (iv) (a) : When butanone reacts with ethylene glycol (a) : This reaction is Wolff-Kishner reduction. The in presence of HCl, it forms a ketal. reagents used for this reduction are NH2NH2/KOH. 124 Chemistry | Class 12

2+ – – 8. (i) (a) HCHO + 2Cu + 5OH HCOO + Cu2O + 3H2O Reddish brown ppt. (ii) (c) : Phosphorus converts a little of the acid into acid chloride which is more reactive than the parent 10. (i) (a) carboxylic acid. Thus, it is the acid chloride, not the – (ii) (b) : HSO is a bulky nucleophile, hence, cannot acid itself, that undergoes chlorination at the a-carbon. 3 attack on sterically hindered ketones. OR (iii) (d) : Aromatic aldehydes and ketones are less (d) : Bromination occurs at a-positions. reactive than the corresponding aliphatic analogues a Br2/P towards nucleophilic addition reactions due to the +R CH3 CH2 COOH CH3CHBr COOH –HBr effect of benzene ring. Further, aldehydes are more Br2/P –HBr reactive than ketones due to +I effect and steric effect of alkyl group. CH3 CBr2 COOH Therefore, the ease of nucleophilic addition will follow (iii) (a) : b-ketoacids are unstable acids. They readily the order : undergo decarboxylation through a cyclic transition state.

OR (a) : Formation of cyanohydrin from an aldehyde or ketone occurs very slowly with pure HCN because it is feebly ionised. This reaction is catalysed by a base. Base generates CN– ion which is a stronger nuclephile NaOH/CaO CH CH CH COOH and readily adds to carbonyl compound. (iv) (b) : 3 2 D OH + HCN CN + H2O CH3 d+ d O H+ OH CH CH CH + Na CO • 3 3 2 3 C O + • CN C C CN CN CH3 9. (i) (b) : All aliphatic aldehydes give red ppt. with (iv) (b) : Electron withdrawing group (–NO2) Fehling’s solution, but ketones do not reduce Fehling’s increases the reactivity towards nucleophilic addition solution. reactions, whereas electron donating group (–CH3) decreases the reactivity towards nucleophilic addition (ii) (c) : Aliphatic aldehydes reduce Fehling’s solution, reactions. but aromatic aldehydes do not. 11. (c) : Highly branched carboxylic acids are less OR acidic than unbranched acids. The +I effect of alkyl (a) : Fehling’s solution is a mild oxidising agent. It groups in branched acid increases the magnitude of cannot oxidise aromatic aldehydes to corresponding negative charge. Thus, –COOH group is shielded carboxylate ion. from solvent molecules and cannot be stabilized by solvation as effectively as in unbranched carboxylic (iii) (b) : CH3CHO and C6H5CH2CHO both are aliphatic aldehydes, hence cannot be distinguished acids. by Fehling’s solution. CH3CHO contains CH3CO– 12. (a) group whereas C H CH CHO does not contain any 6 5 2 13. (b) : Aldehydes have higher molecular weight than CH3CO– group. Thus, CH3CHO will give yellow ppt. with I and NaOH but C H CH CHO will not. parent alkanes as well as polarity in aldehydes shows 2 6 5 2 higher boiling point than parent alkanes. Aldehydes (iv) (d) : Formaldehyde when heated with Fehling’s do not have any hydrogen atom attached directly to reagent, undergo oxidation to give formate ion and the oxygen so they cannot form hydrogen bond with produce reddish brown ppt. of Cu2O. each other. Aldehydes, Ketones and Carboxylic Acids 125

14. (b) : Carbonyl compounds form solid additive 22. (c) : Addition of Grignard reagents to dry ice products with NaHSO3 which are separated out. followed by hydrolysis gives carboxylic acid not The solid bisulphites of carbonyl compounds on ketone. hydrolysis with dilute acid regenerate original carbonyl compounds and thus, this property is used for the purification of carbonyl compounds as well as for their separation. 15. (c) : In p-chlorobenzoic acid, both +R and –I 23. (d) : Aldehydes having a methyl or methylene effect operate together but in m-chlorobenzoic acid group in the a-position or more correctly having only –I effect operates. Therefore, m-chlorobenzoic atleast one hydrogen atom in the a-position undergo acid is a stronger acid than p-chlorobenzoic acid. dimerisation in presence of a base at low temperature 16. (b) : Presence of acid intensifies the partial positive to form b-hydroxy aldehydes called aldols. As charge on carbonyl carbon and hence, activates the benzaldehyde does not have any a-hydrogen hence it group. does not undergoes aldol condensation. + CO+H+ C O H 24. (a) Presence of base activates a-methylene component 25. (c) : Carboxyl group only marginally decreases of the carbonyl compounds by converting them in the electron density at m-position relative to o- and carbanions. p-positions. – → – RCH2CHO + :B RCHCHO + BH 26. (c) : Chlorine atom has –I effect which increases 17. (b) : Due to overall electron-donating effect of the the ionisation of chloroacetic acid and stabilizes the phenyl group, benzoate ion is less stable than formate chloroacetate ion by dispersal of negative charge. In ion. acetic acid, methyl group due to +I effect destabilizes the acetate ion by intensification of negative charge. 18. (b) : Both carbanions (formed in presence of base) and enol form (formed in presence of an acid) act as Hence, chloroacetic acid dissociates to a greater extent nucleophiles and hence add on the carbonyl group of than acetic acid. aldehydes and ketones to give aldols. 27. (c) : The anion left after the removal of a-hydrogen 19. (b) : Boiling points of carboxylic acids are higher is stabilized by resonance effect. due to their tendency to associate and form dimers to 28. (d) : During reaction of carboxylic acids with a greater extent by hydrogen bonding. NaHCO3, CO2 evolved comes from NaHCO3. 20. (b) : Lower aldehydes and ketones are soluble Carboxylic acid is a stronger acid than carbonic acid. in water due to polar effect of C O group which 29. (a) : o-Substituted benzoic acids are generally makes hydrogen bonds with water molecules. As stronger acids than benzoic acid. This is regardless of the size of the aldehydes and ketones increases the the nature (+I or –I) of the substituent. This is called hydrophobic part i.e., alkyl chain increases which ortho-effect and is probably due to a combination of weakens the H-bond formations with H2O molecules steric and electronic factors. and decreases the solubility. 30. (c) : Aromatic aldehydes and formaldehyde do 21. (b) : The –I effect of F is greater than inductive not contain a-hydrogen and thus undergo Cannizzaro effect of Cl and thus fluoroacetate ion is more stabilized reaction. Formaldehyde is more reactive than aromatic to show more tendency to lose proton by its acid. aldehydes.  Get these QUESTIONS in CHAPTERWISE format in